1. Field of the Invention
The present invention relates to an information converting method, an information converting apparatus, and an information reproducing apparatus including such an information converting apparatus. More particularly, the present invention relates to an information converting method and an information converting apparatus, which can convert compressed audio information into transmission information that can be transmitted through a serial data bus, and an information reproducing apparatus including such an information converting apparatus.
2. Description of the Related Art
DVD has an improved record capacity equal to 7 times of that of a conventional CD (Compact Disc).
A so-called DVD video standard intended to mainly record dynamic picture information such as a movie and the like, and a so-called DVD audio standard intended to mainly record audio information with high sound quality are respectively established, as unified standards when the information is digitally recorded on the DVD. They are being distributed to a writer of the dynamic picture information, a writer of the audio information and the like, respectively.
Among them, according to the DVD audio standard, its large capacity enables, for example, control information for a so-called surround reproduction having realism and audio information of three or more channels to be reproduced at one time, which enables the surround reproduction to be enjoyed.
On the other hand, as a new standard intended to transmit information in a real time manner through a serial bus between a plurality of information processors (for example, between a personal computer and a digital vide camera or MD (Mini Disc) or the like), a so-called IEEE 1394 standard is published (a formal name of which is “IEEE Std. 1394-1995 IEEE Standard for a High Performance Serial Bus”). Then, a digital vide camera, a personal computer and the like having serial ports based on this standard are manufactured.
This IEEE 1394 standard is standardized such that a plurality of information processors (hereafter, which are merely referred to as “nodes”) are connected through a serial bus to each other, and information transmissions corresponding to a plurality of channels can be executed in a time sharing manner between those respective nodes. The standard is also standardized such that the information transmissions can be done by using a maximum of 63 different channels within a system connected through one serial bus.
Here, the IEEE 1394 standard is standardized such that an initialization of a serial bus referred to as a so-called “bus reset” is executed when another node is newly connected to a group of nodes already connected through the serial bus to each other (namely, at a time of a bus connection) or when one node is disconnected from the group of nodes (namely, at a time of a bus disconnection). So, associated with the bus reset, the following processes are executed to thereby establish a connection manner of a new serial bus (hereafter, the connection manner is referred to as a “topology”).    (1) In conjunction with the occurrence of the bus reset, a node that detects the occurrence of the bus reset (namely, a node to which another node is newly connected, or a node from which the a connection until that time is disconnected) sends out a bus reset signal indicative of the occurrence of the bus reset to all nodes connected to the serial bus.    (2) After the bus reset, a tree identification is carried out for connecting the respective nodes on a tree structure. Then, a node located at a vertex of the connected tree structure is recognized as a “route node”.    (3) Next, the recognized route node makes each node recognize an identification number (ID number) peculiar to each node to identify each node within the tree structure.    (4) Next, communication states of all the nodes within the established tree structure (e.g., used channels and later-described transmission occupation time periods of the respective nodes) are managed. Then, an IRM (Isochronous Resource Manager) node is set which is a node for indicating a currently used channel and a transmission occupation time period currently occupied by each node in such a manner that those can be recognized by the other nodes.    (5) Finally, a “bus manager node” is set which is a node for managing the information transmission states of all the nodes.
A new topology after the bus reset is established through the above-mentioned processes at the five stages.
When the information is actually transmitted after the establishment of the topology, a “transmission node” implying a node which starts transmitting the information refers to a current communication state of another node with respect to the IRM node. If a channel and a transmission occupation time period desired to be used by the transmission node can be used, the transmission node obtains a right to transmit the information (actually, the transmission node reserves the channel to be used by the transmission node and the later-described transmission occupation time period) and starts transmitting the information. At this time, immediately before transmitting the information, the transmission node transmits to the IRM node the fact that the indication of the communication state in the IRM node is to be rewritten (namely, since the transmission node starts transmitting the information, the channel under the usage and the transmission occupation time period on the serial bus are changed. Thus, it is necessary to rewrite the content of the indication to a new communication state after this change). The IRM node receiving it executes a process for updating the content of the indication, respectively. After that, the content of the indication after the update can be referred to by the other nodes, respectively.
Next, the transmission occupation time period will be schematically described below.
In the IEEE 1394 standard, the information from the respective nodes is collectively transmitted for each unit referred to as an “isochronous cycle” (which implies one cycle generated by dividing the area on the serial bus in a time sharing manner). This isochronous cycle includes an isochronous transmission area, which includes the information transmitted synchronously with the information included in the other isochronous cycles (actually, video information, audio information or the like), and an asynchronous transmission area, which includes the information transmitted asynchronously with and independently of other information (actually, control information to control an output of the video information or the audio information, and the like). Then, the information within the isochronous transmission area is divided in a time sharing manner for each different channel. So, different information is transmitted for each channel.
At this time, it is standardized that a temporal length of the isochronous transmission area within one isochronous cycle is 100 μsec at the maximum, in the isochronous transmission area. Thus, it is necessary that a total of time periods occupied by the information assigned to each channel within one isochronous transmission area for its transmission is also equal to or less than 100 μsec. At this time, the transmission time period occupied by one channel within the isochronous cycle is the above-mentioned transmission occupation time period.
In addition, this transmission occupation time period may be referred to as a “utilization band of a serial bus”, depending on a case, or may be referred to as a “utilization capacity of a serial bus”. On the other hand, if the temporal length of the isochronous transmission area is less than 100 μsec (including a case of zero) within one isochronous cycle, a time period within the isochronous cycle other than the isochronous transmission area is used only as the synchronous transmission area.
According to the IEEE 1394 standard having the above-mentioned schematic configuration, a large capacity of information can be quickly transmitted irrespectively of an attribute of the video information, the audio information or the like in the transmission information to be transmitted, and for example, the copy control information and the like can be transmitted in addition to the transmission information. Thus, it is also possible to transmit the information while perfectly protecting a copyright with regard to the transmission information, for example.
However, the IEEE 1394 standard is not designed to quickly transmit the audio information recorded on an optical disc, such as DVD based on the above-mentioned DVD audio standard or the like, while protecting the copyright.